A conventional configuration for a deposition reactor is an open-ended, substantially tube-shaped chamber, a portion of which is mounted within a furnace. In a deposition process, a substrate is placed in a heated portion of the reactor and appropriate reactant gases are introduced to the reactor such that they pass over the substrate. For example, to deposit an epitaxial layer of GaAs on a GaAs substrate, the reactant gases contain GaCl and AsH.sub.3, and the substrate is heated to about 700.degree. C. Additionally, controlled amounts of impurities may be introduced during the deposition, for example, so as to form N or P doping in the epitaxial film.
A common objective of an epitaxial growth process is the formation of a single crystalline film having either a high purity or a highly controlled concentration of impurities. However, this requires a carefully controlled deposition sequence and a relatively low level of contamination. A common source of contamination is the material which was deposited on the tube walls in prior deposition sequences.
For example, following the deposition of a relatively heavily doped film, a stringent cleaning of the reactor tube is necessary before a lightly doped or high purity film can be grown. The portion of the tube surrounded by the furnace is conventionally cleaned by pushing HCl vapor through the tube while heating at about 700.degree.-900.degree. C. The unheated portions of the reactor tube, however, are not cleaned by this process and can remain a source of contamination in future depositions. Satisfactory cleaning of the unheated portions is generally accomplished by disassembly of the reactor tube from the furnace so that the contaminated parts can be immersed in an appropriate etching solution. In conventional deposition apparatus this represents a relatively inefficient, time-consuming procedure.